FXTH870xD
Sensors
Freescale Semiconductor, Inc.
137
14.2.3
Definition of Signal Ranges
Each measured parameter (pressure, voltage, temperature, acceleration) results from an ADC10 conversion of an analog signal.
This ADC10 result may then be passed by the firmware to the application software as either the raw ADC10 result or further
compensated and scaled for an output between one and the maximum digital value minus one. The minimum digital value of zero
and the maximum digital value are reserved as error codes.
The signal ranges and their significant data points are shown in
Figure 113
. In this definition the signal source would normally
output a signal between S
INLO
and S
INHI
. Due to process, temperature and voltage variations this signal may increase its range
to S
INMIN
to S
INMAX
. In all cases the signal will be between the supply rails, so that the ADC10 will convert it to a range of digital
numbers between 0 and 1023. These digital numbers will have corresponding D
INMIN
, D
INLO
, D
INHI
, D
INMAX
values. The ADC10
digital value is taken by the firmware and compensated and scaled to give the required output code range.
Figure 113. Measurement Signal Range Definitions
Digital input values below D
INMIN
and above D
INMAX
are immediately flagged as being out of range and generate error bits and
the output is forced to the 0 value.
Digital values below D
INLO
(but above D
INMIN
) or above D
INHI
(but not D
INMAX
) will most likely cause an output that would be less
than 1 or greater than 510, respectively. These cases are considered underflow or overflow, respectively. Underflow results will
be forced to a value of 1. Overflow results will be forced to a value of 510.
SENSOR
ANALOG
ADC10 RAW
DIGITAL
CALCULATED
DIGITAL
(9-BIT EXAMPLE)
(10-BIT CONVERSION)
VOLTAGE
SIGNAL
SOURCE
ADC10
FIRMWARE
ROUTINE
511
510
0
1
256
0
1023
512
V
DD
/2
V
DD
V
DD
S
INMAX
S
INHI
S
INMIN
S
INLO
D
INMAX
D
INHI
D
INLO
D
INMIN
NORMAL CASE
UNDERFLOW
LOWER ERROR CASE
FORCE
OUTPUT
TO ZERO
CASE
OVERFLOW
CASE
FORCE
OUTPUT
TO 511
UPPER ERROR CASE
Содержание FXTH870 D Series
Страница 86: ...FXTH870xD Sensors 84 Freescale Semiconductor Inc Figure 57 Data Flow For Measurements...
Страница 170: ...FXTH870xD Sensors 168 Freescale Semiconductor Inc 19 Package Outline Figure 127 QFN Case Outline...
Страница 171: ...FXTH870xD Sensors Freescale Semiconductor Inc 169 Figure 128 QFN Case Outline...
Страница 172: ...FXTH870xD Sensors 170 Freescale Semiconductor Inc Figure 129 QFN Case Outline...
Страница 173: ...FXTH870xD Sensors Freescale Semiconductor Inc 171...